[COFF] Fix section name for constants larger than 64 bits on Windows

APIntToHexString returns wrong value ("0000000000000000ffffffffffffffff")
for integer larger than 64 bits, and thus
TargetLoweringObjectFileCOFF::getSectionForConstant returns same section name
for all numbers larger than 64 bits. This patch tries to fix it.

Differential Revision: https://reviews.llvm.org/D66458
Patch by Senran Zhang

llvm-svn: 369610